Enantiopure mono hydroxyl syn or anti azido/alkoxy-1,2-diols are valuable building blocks for the bioactive pharmaceuticals. It is a known fact that enantiomerically pure drugs have numerous advantages over racemic drug mixtures including advantages, such as, fewer side effects and greater potency, which result in part from the ability of living systems to differentiate between enantiomeric compounds. Access to these building blocks is provided by several routes including asymmetric reduction of aryloxy ketones or the ring opening of enantiopure terminal epoxides.
Ring opening of terminal epoxides in presence of a chiral catalyst known in the art are used to resolve single epoxide.
An article titled “Asymmetric Processes Catalyzed by Chiral (Salen) Metal Complexes” by Jay F. Larrow and Eric N. Jacobsen in Topics Organomet Chem (2004) 6: 123-152 relate to catalytic asymmetric ring opening or kinetic resolution of meso and racemic terminal epoxides using variety of synthetically useful nucleophiles to obtain enantiopure dissymmetrically substituted epoxides. The catalyst is selected from chiral (salen)Co(III) and Cr(III) complexes. An article titled “Asymmetric Catalytic Synthesis of α-Aryloxy Alcohols: Kinetic Resolution of Terminal Epoxides via Highly Enantioselective Ring-Opening with Phenols by Joseph M. Ready and Eric N. Jacobsen in J. Am. Chem. Soc. 1999,121, 6086-6087 relates to phenolytic kinetic resolution of terminal epoxides in presence of (salen)Co(III) catalyst to generate 1-aryloxy-2-alcohols.
The aforementioned kinetic resolution technique, however, results in α-aryloxy alcohol with only one stereo centre.
Further, the processes described in the art to synthesize functionalized α-Aryloxy alcohols involve higher temperature conditions and protection/deprotection of various functional groups leading to multistep reaction sequences thereby limiting the overall yield and the enantioselectivity of the process particularly unsuitable for the atom economic synthesis.
In context with the growing demand for enantiopure α-azido/alkoxy alcohols as intermediate in preparation of enantiomeric pure drugs and to expand the scope of stereoselective ring opening of racemic terminal epoxides, present inventors have explored the possibility of improving upon the existing kinetic resolution technique to provide enantiopure α-Aryloxy-α′-Azido/Alkoxy alcohols with two stereocentres.
The previous work published by the applicant in the article titled “Co(III)(salen)-catalyzed HKR of two stereocentered alkoxy- and azido epoxides: a concise enantioselective synthesis of (S,S)-reboxetine and (+)-epi-cytoxazone” by R. Santhosh Reddy, Pandurang V. Chouthaiwale et. al in Chem. Commun., 2010, 46, 5012-5014 discloses hydrolytic kinetic resolution (HKR) of racemic syn- or anti- alkoxy- and azido epoxides catalyzed by Co(salen) complex to obtain enantioenriched syn- or anti- alkoxy- and azido epoxides and the corresponding 1,2-diols.
The present inventors have observed that synthesis of certain bioactive molecules is still difficult using the previously known kinetic resolution technique with water as nucleophile. Moreover, selective protection of alcohols is generally tedious which may increase the number of steps in the preparation of bio active products.
In view of the above, there remains a need to provide an economical process that can provide monohydroxy protected syn or anti azido/alkoxy-1,2-diols as valuable “building blocks” for the bioactive pharmaceuticals.